Allow customization of issue generated branch names

[CarterQC]

Currently gitpod only allows for creating a workspace and branch from an issue with this naming scheme:
<your-username>/<issue-title>-<issue-number>

But since many teams use different branch naming schemes, it would be very nice to be able to customize this. Ideally something we could just set in the .gitpod.yml with optional pre-defined variables (issue-title, username, issue-number, etc.) available that could be interpolated in a format that gitpod could parse.

For example:

branch_naming:
    issue: "task-<issue-number>/<issue-title>"

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[gtsiolis]

Although sensible defaults sounds optiomal, this could be a nice small improvement which could be useful for larger groups with stricter development guidelines. Additionally, this could be better as part of the new project settings instead of the .gitpod.yml configuration. cc @jldec

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.